dt-bindings: serial: example cleanup

dt-bindings: serial: example cleanup

Adjust example DTS indentation to match recommended style of 4-spaces
and use lower-case hex for address in reg.  No functional change.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20230124091916.45054-10-krzysztof.kozlowski@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>